With the development of Internet of Things (IoT) and Smart Home, environment sensing techniques frequently applied at home are in continuous progress; among these techniques, the gas sensing technique is strongly demanded. The gas sensing technique may be applied not only for monitoring a residential environment but also for monitoring an environment at offices, factories, hospitals, or any other public areas. A gas sensor may be employed to detect whether pernicious gas exists in the surroundings, and an alert may be issued if the pernicious gas in the surroundings is detected, so as to prevent human beings from inhaling the pernicious gas. Most of the existing gas sensors are required to be operated at a high and constant temperature. Since the heat energy of the gas sensing layer is easily dissipated, the gas sensing layer is required to be constantly heated by a heater, such that the gas sensing layer may remain at a high temperature. As such, electricity may be continuously supplied to the heater, thus leading to significant electrical energy consumption. Besides, when the gas sensing layer disposed on a support film is being heated by the heater, it is easily for the support film to be cracked or warped, which lessens the accuracy and reliability of the gas sensor.
For instance, the gas sensor is integrated with a temperature sensor, a moisture sensor, an air quality sensor, or any other sensor to create a multi-functional environment sensor, so as to monitor the gas, the temperature, the moisture, or the air quality of the environment and thereby improve the safety and comfort of the surroundings. In view of the above, the environment sensing techniques may be developed in order to satisfy the requirements for multi-functional monitoring. Hence, how to develop the gas sensor characterized by high sensing accuracy, high reliability, and low electrical power consumption or develop the multi-functional environment sensor has become one of the issues to be resolved in the pertinent field.
FIG. 1 is a schematic view illustrating a conventional gas sensing apparatus. With reference to FIG. 1, a gas sensing apparatus 10 heats a gas sensing film 12 through a heater 11, so as to increase the variation level of the electrical resistance generated by the gas sensing film 12 in response to the variations in the concentration of target gas. Through measuring the amount of electrical current input to the gas sensing film 12 by an electrode 13, the variation level of the electrical resistance of the gas sensing film 12 may be calculated, and the variations in the concentration of target gas around the gas sensing apparatus 10 may be learned.
FIG. 2 is a schematic view illustrating a conventional micro-electromechanical semiconductor gas sensor. With reference to FIG. 2, a first film 21 and a second film 22 connected to the first film 21 of the micro-electromechanical semiconductor gas sensor 20 are penetrated by plural vias that are not covered by a heater 23 nor by a sensing electrode 24. Hence, heat may be dissipated to the surroundings through the vias, so as to prevent the first film 21 and the second film 22 from being warped and distorted by thermal stress.
FIG. 3 is a schematic view illustrating a conventional micro-electromechanical oxygen sensor, wherein a temperature sensor 32, a heater 33, and a sensing material layer 34 are disposed on a film 31. The heater 33 timely heats the sensing material layer 34 according to the temperature detected by the temperature sensor 32 to control the temperature of the sensing material layer 34.
FIG. 4 is a schematic view illustrating a conventional micro-electromechanical gas sensor. With reference to FIG. 4, a porous layer 42 is embedded in a mono-crystalline substrate 41 of a micro-electromechanical gas sensor 40, and a lower insulation layer 43 covers the mono-crystalline substrate 41 and the porous layer 42. In addition, a heating layer 44 is disposed on the lower insulation layer 43 and right above the porous layer 42. Hence, the porous layer 42 may stably support the heating layer 44 and prevent the lower insulation layer 43 from being warped and distorted by thermal stress while the micro-electromechanical gas sensor 40 is being operated at a high temperature. Since the heating layer 44 is disposed right above the porous layer 42, favorable thermally insulating effects may be accomplished.
In light of the foregoing, common micro-electromechanical environment sensors may keep the environment sensing layer to remain at a constant temperature if a heating device is employed to continuously heat the environment sensing layer.